Method of applying insulator coating



Aprifi16,1935. L, E, PQWER 1,997,874

METHOD OF APPLYING INSULATOR COATING Original Filed Sept. 29, 1926 7 '7! 5/74? A". ZUJWEZ Patented Apr. 16, 1935 UNITED STATES PATENT OFFICE 1,991,8'i4 METHOD or APPLYING INSULATOR COATING Laurence E. Power, Milwaukee, Wis., assignor, by mesne assignments, to Allen-Bradley Company, Milwaukee, Wis., a corporation of Wisconsin 4 Claims.

This invention relates to certain newrand useful improvements in apparatus for and method of'applying insulator coating and is a division of my application filed September 29, 1926, Se-

5 rial No. 138,494.

Heretofore, ithas been customary to line housings and cabinets for electrical controls by gluing sheet asbestos or other insulating material thereto which has proven objectionable in that sheet asbestos is not only expensive but costly to apply and further, its resistance to an electrical arc is unsatisfactory.

Therefore, this invention contemplates as one of its objects the provision of an improved method of lining cabinets which is comparativelycheap to apply and whereby a very efficient insulating surface is supplied capable of ofiering an excellent resistance to destructive arcing forces.

Another object of this invention resides in the provision of an improved method of applying an insulating surface to walls which consists in simultaneously spraying two solutions to merge just prior to or as they engage the surface to be lined, the solutions having the characteristic of thickening immediately upon contact with each other.

And a still further object of this invention resides in the provision of an improved device whereby two solutions may be so applied to a surface as to merge just at or prior to their engagement therewith.

With the above and other objects in view which will appear as the description proceeds, my invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being under-' stood that such changes in the precise .embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

In the accompanying drawing, I have illustrated one complete example of the physical embodiment of my invention constructed according to the best mode I have so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a top plan view of a compound air brush or spray of the type employed in conjunction with my improved insulator lining and method of applying the same;

Figure 2 is a view, partly in section and partly in elevation, taken through one unit of the compound spray on the plane of the line 2--2 of Figure 1, and

Figure 3 is a view taken transversely through REISSUED Figure 2 on the plane of the line 33 and illustrating one of the control valves of a spray unit.

The present conventional manner of insulating the interior wall surfaces of metal cabinets employed ,in connection with switches and other electric apparatus, is to line the same with asbestos paper. While this manner of lining cabinets has been in vogue for many years and meets with approval by the board of underwriters, it is open to many serious objections such as the inability of asbestos paper to satisfactorily resist an electric arc and also that it is very expensive to apply, both from the standpoint of material and labor.

This invention, therefore, contemplates the elimination of the cumbersome manner of lining cabinets heretofore used, by the substitution of an improved insulating solution and apparatus for and method of applying the same wherein a better insulating lining is obtained at a considerably reduced cost.

This objectionable type of lining is replaced by one composed of a solution of glue, water and powdered mica applied to the surface and allowed to dry. It has been found from experience that the above solution in the following proportions:

Parts by weight Glue 3 Water 5 Powdered mica 4 withstands the arc test in a very satisfactory manner, but is open to the objection that when 3 applied to an inclined surface it has a tendency to run, making its application tedious and dimcult except on a level surface.

The glue employed in the above solution is preferably made according to the following formula:

although it is to be understood that any glue capable of providing the necessary adherence may be used. The mica employed is preferably a two hundred mesh.

Sodium silicate, or water glass, may be added to the solution of glue, water and mica, when the following approximate proportions are prefer-- Sodium silicate (ordinary commercial grade)- 5 The glue andwater are first mixed, the powdered mica then thoroughly stirred therein and the sodium silicate or water glass added. Immedi ately upon the addition of the sodium silicate, the

I viscosity of the solution increases due to the precipitation of colloids, or gel formations.

To facilitate the application of the solution to a surface, the same is heated to a working temperature preferably under degrees Fahrenheit, at which temperature the same may be applied by means of a brush. Experience has demonstrated that a solution applied as above has the characteristic of remaining where placed on a surface without showing a tendency to run irrespective of the inclination of the surface.

However, a solution having sodium silicate therein is difficult to apply in a smooth even coating, and this objectionable feature is overcome by spraying the solution in two streams, one including glue, water and mica, and the other sodium silicate, the streams preferably coming together just prior to or as they strike the surface to be lined. When applied in this manner, any desired thickness may be applied and the solution shows no tendency to run due to the immediate increase in viscosity thereof as the sodium silioate comes into contact with the glue, water and powdered mica.

When the solution is sprayed in divided form the following approximate proportions may be employed:

Parts by weight Glue Water 20 Mica--- 5 Sodium silicate 5 The proportion given above may be varied considerably and still produce excellent results, as it is difficult in actual practice, where the materials are sprayed separately, to maintain the exact proportions between the glue,-water and mica, and sodium silicate. It is desirable, however, to avoid a large excess of sodium silicate over that which is necessary to produce the desired increase in viscosity as sodium silicate is not a good insulator at high temperatures.

In the accompanying drawing, to which reference is directed, is illustrated the novel spraying apparatus which may be employed to apply my solution, which is preferably divided with the sodium silicate in one container, not shown, and the glue, water and mica in another, not shown.

The spraying apparatus consists of two spray guns or brushes 5 and 6 of complementary construction connected by a plate or bridging member l fixed thereto by screws or other fastenings 8. As the spray guns or brushes are identical in construction, the following description refers to but one.

The spray gun consists of a casting 9 having a horizontal barrel It) the outer end of which is exteriorly threaded, as at H, to adjustably receive a spray nozzle or end cap l2. The spray nozzle is provided with a central spray orifice l3 of conical shape at its inner end to cooperate with a jet l4 communicating with an air passageway l5 extending throughout the length of the barrel to one side of a valve I6 mounted in the rear end I! thereof. The nozzle or end cap I2 has the jet l4 projecting into the conical shaped portion of its orifice l3 but spaced therefrom to provide a passage communicating with a chamber 18 from which one or more passages is lead to a threaded bore 20 with which a supply tube 2| leading from the container, not shown, filled with the solution, is connected.

A handle or grip 22 is fixed to the end ll of the barrel and has an air supply tube 23 extended therethrough which leads from a source of air under pressure so that operation of the valve 86 by a control knob 24 causes the air to pass through the passage l5 and out through the orifice I3 creating a suction in the chamber H8. The air passes through the orifice I3 to produce an injector effect and draws the solution from the container, not shown, through the tube 26 to be expelled through the jet l3 in a spray.

The axes of the bores of the orifice I3 of the two spray guns intersect in the manner illustrated in Figure 1 so that the stream or spray 25 of the gun 5 commingles, as at 26, with the stream or spray 21 of the other gun 6, the point of commingling being either at the surface 28 which is being lined, or just before striking the same. Thus, assuming the stream 25 to be sodium. silicate and the stream 21 glue, water and mica, the commingling thereof at the point 26 causes a change in the viscosity of the solution, and thereby prevents its running without effecting its application in an even coating.

As the fluids making up the solution have a tendency to continue flowing after the air valve i6 is closed, each line 21 has a valve 29 therein which is normally urged closed by a suitable spring 30 connected with the stem 3| of the valve member. Also connected with the valve stem is an operating member 32 to which a finger receiving loop 33 is connected to permit the operator to hold the spray gun with the index finger through the loop 33 and the thumb engaging the button 24. Thus, in operation, the operator holds a spray gun in each hand and exerts a pull on the straps 33 and depresses the buttons 24.

From the foregoing description taken in connection with the accompanying drawing, it will be readily evident to those skilled in the art to which this invention ja'p'pertains that I provide an improvedinsulating lining .and method of and apparatus for applying the same which very efficiently and satisfactorily insulates the interior surface of cabinets andthe like, and has the ability to successfully withstand destructive arcing forces.

What I claim as my invention is:

1. The hereindescribed method of forming a dielectric insulating composition and lining a wall therewith, which consists in simultaneously directing a spray of glue and water solution containing mica in suspension and a spray of a solution of sodium silicate toward each other and on the wall, the solutions commingling to produce a precipitate in the form of a substantially immobile composition lining the wall.

2. The hereindescribed method of forming a dielectric insulating composition and lining a wall therewith, which consists in simultaneously spraying a glue solution and a colloidal solution having the ability to cause a precipitation of colloids in the glue solution, onto the wall and toward each other, so that the solutions oommingle at or near the wall surface.

3. The hereindescribed method of forming a dielectric insulating composition and lining a wall therewith, which consists in simultaneously spraying onto a wall and toward each other, so that they commingle at or near the wall surface, a solution of sodium silicate and a colloidal solution from which the colloids will be precipitated 10 by the sodium silicate solution.

4. The hereindescribed method of forming a dielectric insulating composition and lining a wall therewith, which consists in simultaneously spraying a glue solution and a colloidal solution having the ability to cause a precipitation of colloids in the glue solution, onto the wall and toward each other, so that the solutions commingle at or near the wall surface, one of said solutions containing an inert insulating material.

LAURENCE E. POWER. 

